1. Technical Field
The present invention relates to a voltage measuring apparatus for detecting an output voltage of an assembled battery in which a plurality of unit cells are connected in series and a desired voltage is output.
2. Background Art
For example, a hybrid vehicle includes a high-voltage battery as a driving power source of a motor. In the high-voltage battery, a plurality of unit cells of a secondary battery (storage battery) such as a lithium battery or a nickel hydride battery are connected in series, thus a high voltage is obtained.
It is necessary to check a charge state every each unit cell so that a secondary battery does not become an overdischarge state or an overcharge state. Conventionally, a plurality of (for example, 55) unit cells are divided into, for example, five blocks (that is, one block by 11 unit cells) and a voltage of each of the blocks is measured in real time by an IC for voltage detection disposed every each block.
In this case, in the IC for voltage detection, a voltage of unit cells (for example, 11) of one block is measured and further, an analog voltage signal detected is converted into a digital signal by an A/D converter provided in the IC for voltage detection, and the digital signal is sent to a main microcomputer. Thereafter, by the main microcomputer, when there is the block in which abnormality of a voltage occurs, it is constructed so that a warning is issued and a crew of a vehicle is notified of the voltage abnormality or correction processing of the voltage is performed (for example, see JP-A-2005-62028).
However, in the conventional voltage measuring apparatus, a voltage for A/D conversion used in an A/D converter is generated from a voltage obtained from each unit cell, so that the voltage for A/D conversion may vary and in such a case, an error may occur when a voltage detected in each block is digitized. As a result of this, there is a problem that high-accuracy voltage detection cannot be performed.